1. Field of the Invention
The present invention relates to an electrophoretic display device for displaying migrated charged particles, and a method for addressing the display device.
2. Related Background Art
Various methods are used for output of a line of information since data volume of various information is being expanded in recent years as a result of development of information instruments. In general, output of information is roughly categorized into two groups of display on a cathode ray picture tube or a liquid crystal panel, and hard copy display on a sheet of paper using a printer. Needs of a thin type display device with low power consumption has been increasingly required, and the display device that can correspond to these needs has been aggressively developed and put into the market. However, images such as letters on the screen become hardly distinguishable depending on the view angle of the screen or by the reflection light, or the problem of burden on the vision caused by flickering or low brightness of the light source has not been sufficiently solved. Although the display device using the cathode ray picture tube has more sufficient contrast and brightness as compared with the liquid crystal display device, the display quality of the former is not so sufficient yet in the appearance of flickering as compared with the hard copy display to be described hereinafter. The display device using the cathode ray picture tube has also another problem that it has such a large size that it is not suitable as a portable device.
While the hard copy display has been considered to be of no use by utilizing electronic information, a vast amount of hard copy outputs are actually used. This is because, in addition to the problem of the image quality of information on the screen, resolution of the screen is substantially as low as about 120 dpi as compared with resolution of print-out on a sheet of paper (usually 300 dpi or more). Accordingly, display image on a panel gives a larger burden on the vision as compared with the hard copy display. As a result, a line of information is often output as a hard copy, even when the image is distinguishable on the display. It is also the reason why the hard copy display is used together even when the panel display is possible, that a number of the hard copy information can be arranged with no restriction of the display area depending on the display size contrary to the panel display, the information lines can be rearranged without any complicated hard ware operation, or the information lines can be sequentially confirmed. In addition, the hard copy display requires no energy, and is so excellent in handiness that the lines of information can be reconfirmed anytime and anywhere, so long as the information size is not extremely large.
While the hard copy display has many advantages over the panel display except moving images or provided that hazardous rewriting is not required, the hard copy display has a drawback that a lot of paper is consumed. Accordingly, development of recording media capable of rewriting (recording media capable of many recording and erase cycles of the images that are high recognizable by the vision, and requires no energy for holding of display images) has been actively carried out. The third display method capable of rewriting that succeeds the characteristics of the hard-copy is called herein as a paper-like display.
The essential conditions of the paper-like display are being capable of rewriting, requiring no or small energy for retaining display images (memory characteristics), and being excellent in handiness and display image quality. Display methods that are currently considered to be the paper-like display include reversible display media using matrix systems of low molecular weight organic molecule and polymer resins (disclosed in, for example, Japanese Patent Laid-Open Nos. 55-154198 and 57-82086) in which images are recorded and erased with a thermal printer head. While this system is partly utilized as display portions of a prepaid card, it involves some problems that contrast is not so high and the repeating number of recording and erasing is relatively as small as about 150 to 500 times.
Another display method that can be utilized as the paper-like display include an electrophoretic display device (U.S. Pat. No. 3,612,758). The electrophoretic display device is also disclosed in Japanese Patent Laid-Open No. 9-185087.
This display device comprises a dispersion system composed of colored and charged particles dispersed in an insulation liquid and a pair of electrodes opposed across this dispersion system. When a voltage is applied to the dispersion system through the electrodes, a Coulomb force allows the colored and charged particles to be absorbed to the electrode at the side having an opposite electric charge to the charge of the colored and charged particles themselves, by taking advantage of the electrophoretic property of the colored and charged particles. Images are displayed by taking advantage of the color difference between the colored and charged particles and dyed insulation liquid. In other words, the color of the colored and charged particles is observed when the colored and charged particles are absorbed on the surface of the first light-permeable electrodes proximal to an observer. When the particles are absorbed on the surface of the second electrode distal to the observer, on the contrary, the color of the insulation liquid, which has been colored to have optical characteristics different from the colored and charged particles, is observed.
However, no dyes or ions should be mixed with the insulation liquid in such an electrophoretic display device. Presence of these chromatic substances tends to act as instability factors in electrophoretic operations due to exchange of additional charges, to cause deterioration of the performance, service life and stability as the display device.
For solving these problems, Japanese Patent Laid-Open No. 49-5598 and Japanese Patent Publication No. 10-005727 have disclosed a display device in which a pair of electrodes comprising first and second display electrodes are arranged on the same substrate, and the colored and charged migration particles are made to transfer toward the horizontal direction as viewed by an observer. A voltage is applied through a transparent insulation liquid, and the images are displayed by allowing the colored and charged particles to horizontally transfer toward the direction parallel to the surface of the substrate between the first and second display electrodes by taking advantage of the electrophoretic property of the particles.
The insulation liquid is transparent in this in-plane (transfer) type electrophoretic display device, and the first display electrode has a color different from the color of the second display electrodes when viewed from the observer""s side. The color of one of the electrodes is made to coincide with the color of the charged particles. For example, when the first electrode, the second electrode and the charged particles are colored black, white and black, respectively, the second electrode is exposed with white color when the charged particles are distributed on the first electrode, and the second electrode is colored black when the charged particles are distributed on the second electrode.
The methods for electrically addressing the display device on which pixels are arranged in a matrix are roughly classified into an active matrix method and a passive matrix method.
In the active matrix method, switching elements such as thin film transistors are formed for every pixel, and the voltage applied for each pixel is independently controlled to one another. This method enables the in-plane (transfer) type electrophoretic display element to be addressed with high display contrast. However, this active matrix method involves the problems that the process cost is high in this method, and forming the thin film transistors on the polymer substrate is difficult due to high process temperature of the thin film transistor. This problem is particularly crucial in the paper-like display since the object is to manufacture a flexible display with low cost. Although a process for forming the thin film transistor on a polymer material to which a printing process is applicable is proposed for solving these problems, possibility of practical use of this technology has not been made clear yet.
The passive matrix method affords a low cost process since the constituting elements required for addressing is only X-Y electrode lines, which can be readily formed on the polymer substrate. A voltage corresponding to a writing voltage may be applied to X-electrode lines and Y-electrode lines crossing to one another at selected pixels, when the writing voltage is applied to the selected pixels. However, image signals are written on a part of peripheral pixels of the selected pixel, or a so-called cross talk phenomenon arises, when one attempts to address the in-plane (transfer) type electrophoretic display device by the passive matrix method, causing very poor display contrast. This is inevitable since the in-plane (transfer) type electrophoretic display device has no definite threshold against the writing voltage.
It is proposed for solving these problems in the electrophoretic display method having in principle no threshold to add a control electrode to the display electrodes in order to realize addressing of the passive matrix using a three electrode construction. Most of the proposals on the three electrode construction are made with respect to vertical transfer electrode type electrophoretic display including those disclosed in Japanese Patent Laid-Open No. 54-085699 (U.S. Pat. No. 4,203,106).
The proposal on the three electrode construction of the in-plane (transfer) type electrophoretic display device is only found in Japanese Patent Publication No. 8-507154 (U.S. Pat. No. 5,345,251). However, the dispersion solution is not transparent but is colored in Japanese Patent Publication No. 8-507154 (U.S. Pat. No. 5,345,251), which is different from the transparent transfer type electrophoretic display device in which the dispersion solution is transparent as the objects of foregoing Japanese Patent Laid-Open No. 49-5598 and Japanese Patent Application Publication No. 10-005727, and the present invention.
Two constructions are disclosed in Japanese Patent Publication No. 8-507154 with respect to the disposition of the control electrodes. FIGS. 41A and 41B show cross sections of the display devices having the two constructions. In the first construction, a control electrode 5a as a third electrode is provided at the second substrate side 2 of the in-plane (transfer) type electrophoretic device (see FIG. 40A). In the second construction, a control electrode 13a is provided as a third electrode between the first display electrode 4 at the first substrate 1 side and a second display electrode 3 (see FIG. 41B).
A fork-shaped first display electrode. In which plural line electrodes are assembled in one pixel, and a fork-shaped second display electrode, in which plural line electrodes aligned between respective lines of the first display electrode, are placed on a first substrate in both of the first and second constructions. A thick film of chromium is coated on the second display electrode 3, leaving a step 22 with a height of about 0.3 xcexcm at the boundary between the first display electrode 4 and the second display electrode 3. The control electrode 5a is formed over the entire surface within the pixel formed on the second substrate 2 opposed to the first substrate 1 with a space of 25 to 116 xcexcm in the first construction. In the second construction, the control electrode 13a is disposed between respective lines of the first display electrode 4 and second display electrode 3 on the first substrate. In FIGS. 41A and 41B, the first and second display electrodes are composed of a single line, respectively, for the convenience of explanation.
The writing operation in Japanese Patent Publication No. 8-507154 will be described using FIGS. 42 and 43. FIG. 42 shows transfer of charged particles, and FIG. 43 shows an applied pulse and change of reflectivity. The cell construction is the same as described in FIG. 41A (1 pixel).
The applied voltage level to be described hereinafter was determined by the experiment actually carried out by the inventors of the present invention, and the experimental is not always coincide with that described in Japanese Patent Publication No. 8-507154. This is mainly because the conditions depend on the physical properties such as polarity and the amount of charge of the charged particles used. Accordingly, the applied voltage in the experimental results of the charged particles used by the inventors of the present invention will be described hereinafter for easy comparison with the description of operations in the present invention.
While a colored liquid may be used as the insulation liquid in the Japanese Patent Publication No. 8-507154, a transparent insulation liquid is used in the description hereinafter for easy comparison with the description of operation according to the present invention. The method for obtaining the display contrast is also described in the same construction as used in the embodiment of the present invention, wherein the migration particles are colored black, the first display electrode is colored black, and the second display electrode are colored white.
The charged particles are positively charged, and the second display electrode 3 is used as a common electrode. An addressing voltage Vd is applied to the first display electrode 4, and a control voltage Vc is applied to the control electrode 5a with reference to an earth potential of the second display electrode 3 as a reference.
The time period Ta corresponds to a white holding state. The arrow in FIG. 43 shows a vector of an electric field in the cell. Transfer of the charged particles 6 collected on the first display electrode 4 toward the second display electrode 3 is suppressed by a step 22 provided between the first display electrode 4 and the second display electrode 3. The particles are stabilized by being compressed at the display electrode side by applying a holding voltage Vc (=+250V) applied between the first display electrode 4 and the control electrode 5a, thereby maintaining a white display state having a reflectivity (R) of about 70%. The addressing voltage Vd (=5V) applied in the holding state serves for suppressing the tendency of the charged particles in the vicinity of the step to be transferred toward the first display electrode in the black display state.
An addressing voltage (Vd) of +50V and a control voltage (Vc) of +50V are applied during the writing period Tb. Suppression of the charged particles by the control voltage is released by setting the potential of the first display electrode 4 to be the same as the potential of the control electrode 5a, and all the charged particles 6 are horizontally transferred toward the second display electrode along the display electrode face by jumping over the step, thereby rapidly reducing the reflectivity R.
The charged particles are compressed toward the display electrode side during holding period Tc of the black state display by applying a holding voltage (Vc) of +250V, thereby holding the black display state having a reflectivity of about 5%.
The passive matrix addressing method disclosed in Japanese Patent Publication No. 8-507154 will be then described with reference to FIGS. 68A to 68C, and FIGS. 69D to 69G. A in-plane (transfer) type electrophoretic display device in which the pixels are arranged in a mxc3x97n matrix with a column and row numbers of m and n, respectively. Signal electrode lines (m) are aligned along the column direction, and scanning electrode lines (n) are aligned along the row direction of the pixel array, respectively, so as to cross at right angles to one another. Each signal electrode line is connected to the control electrode 5a of each pixel, and each scanning electrode line is connected to the first display electrode 4 within each pixel at each crossing point. The second display electrode 3 is fixed to an earth potential as a common electrode.
Firstly, all the charged particles 6 are collected on the first display electrode by applying an addressing voltage (Vd) of xe2x88x9250V on all the scanning lines, and a control voltage (Vc) of 0V on all the signal lines (FIG. 68A, overall erase). Then, the scanning lines are sequentially selected along the Y-direction from the upper side for writing. An addressing voltage (Vd) of +50V is applied to the scanning lines during the selected period (writing period), and a control voltage (Vc) of +250V is applied to the signal line corresponding to selected pixels The charged particles are transferred toward the second electrode side by climbing up the step for writing (FIG. 68B) in the selected pixels, by applying an addressing voltage (Vd) of +50V between the display electrodes. While an addressing voltage (vd) of +50V is applied in the un-selected pixels, the charged particles are compressed toward the first display electrode by applying a control voltage (Vc) of +250V to prevent transfer (writing) of the charged particles (FIG. 68C).
An addressing voltage (Vd) of +5V is applied, on the other hand, to the scanning line during the un-selected period, and a control voltage (Vc) of +50V or +250V is applied to the signal line (FIGS. 69D to 69G). The display state does not change in either case since the charged particles are compressed onto the display electrode face by the control voltage.
Writing using the passive matrix type addressing method can be executed as described above in the in-plane (transfer) type electrophoretic display device having no thresholds.
However, the in-plane (transfer) type electrophoretic display device disclosed in Japanese Patent Publication No. 8-507154 has involved the following problems. The problems will be described hereinafter with reference to FIG. 70.
The step height is restricted to be not so high in the first construction. When the step height is too high, a part of the charged particles cannot climb over the step and remain at the bottom of the step when the charged particles are transferred during the selected period, thereby decreasing the display contrast (FIG. 70A). The step height should be restricted to be approximately the same as the particle size of the charged particles, in order to prevent the particles from being remained behind.
The effect of the step for suppressing transfer of the charged particles by the step becomes insufficient since the step height is restricted. Consequently, a part of the charged particles are transferred by jumping over the step because the step height is low (FIG. 68C), when transfer of the charged particles should be suppressed by applying a control voltage Vc while an addressing voltage Vd is applied during the selected period. As a result, a cross-talk phenomenon is caused to arise a crucial problem that the display contrast becomes poor (FIG. 70B).
Although the charged particles can be suppressed to a certain extent by sufficiently increasing the control voltage Vc, an ill effect of increase of the applied voltage is caused, besides arising an another problem that electrons injected into the insulation material in the elements by the applied high voltage is left behind after releasing the voltage, and the operation state of the charged particles turns out to be unstable by the unexpected electric field caused by the residual charge.
Another problem of the ill effect of restricted step height is that the area difference between the first display electrode and the second display electrode cannot be determined to be so large due to insufficient step height. This is because the charged particles overflow from the surface of the electrode having a smaller surface area (FIG. 70C) when one attempts to collect the charged particles on the electrode having a smaller surface area, by setting the area difference to be large. Since the display contrast is determined by the area ratio between the first display electrode and the second display electrode, the smaller surface area ratio results in a poor display contrast.
Moreover, restriction effect for transfer of the particles by the step is only effective to the direction from the lower side to the upper side of the step, and transfer from the upper side to the lower side of the step is rather accelerated. Accordingly, writing is only possible toward one direction, or the addressing method is restricted to a unidirectional writing after an overall reset process in which the charged particles on the entire surface are at first collected to the lower side of the step. Bidirectional writing is impossible, or an addressing for rewriting a part of the screen is also impossible.
It is possible in the second construction to prevent bidirectional transfer of the charged particles during the selected period, by applying a voltage between the display electrode and control electrode for the un-selected pixels. It is also possible to allow the charged particles to be smoothly transferred, by setting the voltage between the display electrode and control electrode to zero for the selected pixels. The step height is not an essential constitution element in these cases.
However, the control electrodes only enables transfer between the display electrodes to be prevented, transfer within the display electrode is uncontrollable.
Accordingly, the charged particles evenly distributed within the display electrode transfers toward the direction repelled by the control electrode by the control voltage applied between the display electrode and control electrode during the un-selected period As a result, the display contrast is remarkably decreased due to partial distribution of the charged particles within the display electrode face as shown in FIGS. 71A and 71B.
Accordingly, it is an object of the present invention for solving the foregoing problems to provide an in-plane (transfer) type electrophoretic display device and a method for addressing the display device, wherein occurrence of cross-talk is suppressed, a passive matrix addressing that enables a good display contrast to be obtained is made possible, and the control voltage required for holding the colored and charged charged particles is largely reduced.
Another object of the present invention is to provide an electrophoretic display device that realizes improvement of contrast, and a method for addressing the display device, wherein the ratio between the area of the first display electrode and the area of the second display electrode can be determined to be larger than that in the conventional display device.
Another object of the present invention is to provide an electrophoretic display device, and a method for addressing the display device, wherein a bidirectional writing is possible besides enabling rewrite of a part of the screen.
The inventors of the present invention have found, as a result of analysis of the foregoing problems and intensive studies, that (a) the first and second constructions involve different sorts of problems to one another, and (b) the problem in one construction can be solved by introducing the construction of the counterpart.
Accordingly, the present invention for solving the foregoing problems proposes an electrophoretic display device having novel constructions to be described hereinafter, and a method for addressing the display devise.
The present invention provides an electrophoretic display device comprising a first substrate; a first display electrode and a second display electrode disposed on the first substrate; a second substrate disposed in opposed relation to the first substrate; a voltage applying means for applying a desired voltage on each electrode; a transparent insulation liquid filled between the first substrate and the second substrate; and a plurality of colored and charged fine particles dispersed in the insulation liquid; the display modes being switched by allowing the colored and charged particles to transfer between the first and second display electrodes, wherein a first control electrode disposed on the second substrate, and a second control electrode disposed at the boundary between the first display electrode and the second display electrode on the first substrate, are provided as the electrodes for controlling transfer of the charged particles.
Also, the present invention provides a method for addressing an electrophoretic display device comprising a first substrate; a first display electrode and a second display electrode disposed on the first substrate; a second substrate to be disposed in opposed relation to the first substrate; means for applying a desired voltage on each electrode; a transparent insulation liquid filled between the first substrate and the second substrate; a plurality of colored and charged fine particles dispersed in the insulation liquid; a barrier wall or a step disposed at the boundary between the first display electrode and the second display electrode; a first control electrode disposed on the second substrate as an electrode for controlling transfer of the charged particles; and a second control electrode disposed at the tip of the barrier wall or at the edge of the step on the first substrate, display modes being switched by allowing the colored and charged particles to transfer between the first and second display electrode, wherein transfer of the charged particles comprises a first process for allowing the charged particles to transfer from one of the display electrodes to the vicinity of the second control electrode, and a second process for allowing the charged particles to transfer from the second control electrode to the other display electrode side by jumping over the barrier wall or the step.
Preferably, the boundary between the first display electrode and the second display electrode comprises a barrier wall or a step, and the second control electrode is disposed at the tip of the barrier or at the edge of the step.
Preferably, a shielding space in which the charged particles are able to enter and exit and which is invisible to an observer of the screen is provided under the display electrode face adjoining to the step and located at the upper side of the step.
Preferably, the voltage signal applied on the first display electrode and the second display electrode, and on the first control electrode and the second control electrode for allowing the charged particles to transfer between the display electrodes is a composite signal comprising a first period for allowing the migrating particles to transfer to the second control electrode, and a second period for allowing the migrating particles concentrated on the second control electrode to transfer to the objective display electrode.
It is preferable that a voltage is applied to the first display electrode, second display electrode and control electrode so that the first process satisfies the relation of (the potential of both display electrodes and the potential of the first control electrode) greater than (the potential of the control electrode), and the second process satisfies the relation of (the potential of the display electrode before transfer and the potential of the first control electrode)xe2x89xa7(the potential of the second control electrode) greater than (the potential of the display electrode as a destination of transfer) for transfer of the positively charged particles, and the first process satisfies the relation of (the potential of both display electrodes and the potential of the first control electrode) less than (the potential of the second control electrode), and the second process satisfies the relation of (the potential of the display electrode before transfer and the potential of the first electrode)xe2x89xa6(the potential of the second control electrode)xe2x89xa6(the potential of the display electrode as a destination of transfer), for transfer of the negatively charged particles in order to induce transfer of the charged particles.
Also, the present invention provides an electrophoretic display device comprising a first substrate; a first display electrode and a second display electrode disposed on the first electrode; a second substrate disposed in opposed relation to the first substrate; a control electrode disposed on the second electrode; means for applying a desired voltage on each electrode; a transparent insulation liquid filled between the first substrate and the second substrate; and a plurality of colored and charged fine particles dispersed in the transparent insulation liquid, display modes being switched by allowing the colored and charged particles to horizontally transfer between the first and second display electrodes,
wherein a barrier wall having a function for almost prohibiting direct in-plane transfer of the charged particles at least toward one direction between the first display electrode and the second display electrode is provided between the first display electrode and the second display electrode.
Also, the present invention provides A method for addressing an electrophoretic display device comprising a first substrate; a first display electrode and a second display electrode disposed on the first substrate; a second substrate disposed in opposed relation to the first substrate; a control electrode disposed on the second electrode; means for applying a desired voltage on each electrode; a transparent insulation liquid filled between the first substrate and the second substrate; a plurality of colored and charged fine particles dispersed in the insulation liquid; and a barrier wall disposed between the first display electrode and the second display electrode and having a function for almost prohibiting direct in-plane transfer of the charged particles at least toward one direction between the first display electrode and the second display electrode, display modes being switched by allowing the colored and charged particles to transfer between the first and second display electrodes using the control electrode, wherein the method for transferring the charged particles toward the direction almost prohibited by the barrier wall is carried out by an indirect transfer comprising a first process for allowing the charged particles to transfer from one of the display electrodes to the control electrode side and, succeeding the first process, a second process for allowing the charged particles to transfer from the control electrode side to the other display electrode side by jumping over the barrier wall in-plane transfer
Preferably, the barrier wall protrudes out of at least one face of the first display electrode face and the second display electrode face, and is constructed of a geometrical step having a height several to several tens times as large as the particle size of the charged particles.
Preferably, the barrier wall is a charged assembly applying an electrostatic repulsion force to the charged particles.
Preferably, the barrier wall is also a charged assembly applying an electrostatic repulsion force to the charged particles.
It is preferable that a shielding space in which the charged particles are able to enter and exit and which is invisible to an observer of the screen is provided under the display electrode face adjoining to the step and located at the upper side of either the first display electrode or the second display electrode.
It is also preferable that a voltage is applied to the first display electrode, second display electrode and control electrode so that transfer of the positively charged particles involves the period satisfying the relation of (the potential of the display electrode that is not a destination of transfer)xe2x89xa7(the potential of the control electrode) greater than (the potential of the display electrode as a destination of transfer), and transfer of the negatively charged particles involves the period satisfying the relation of (the potential of the display electrode that is not a destination of transfer)xe2x89xa6(the potential of the control electrode) less than (the potential of the display electrode as a destination of transfer), in order to induce transfer of the charged particles.
Also, the present invention provides an electrophoretic display device comprising a first substrate; a first display electrode and a second display electrode disposed on the first substrate; a second substrate disposed in opposed relation to the first substrate; means for applying a desired voltage on each electrode; a transparent insulation liquid filled between the first substrate and the second substrate; and a plurality of colored and charged fine particles dispersed in the transparent insulation electrode, display modes being switched by allowing the colored and charged particles between the first and second display electrodes, wherein a control electrode is disposed between the first display electrode and the second display electrode on the first substrate, and the space between the upper face of the control electrode and the surface of the first substrate is larger than the spaces between the upper face of the first display electrode and the surface of the first substrate, and between the upper face of the second display electrode and the surface of the first substrate.
Also, the present invention provides a method for addressing an electrophoretic display device comprising a first substrate; a first display electrode and a second display electrode disposed on the first substrate; a second substrate disposed in opposed relation to the first substrate; a means for applying a desired voltage on each electrode; a transparent insulation liquid filled between the first substrate and the second substrate; a plurality of colored and charged fine particles dispersed in the insulation liquid; a barrier wall or a step disposed at the boundary between the first display electrode and the second display electrode; and a control electrode disposed above the structural barrier wall, display modes being switched by allowing the colored and charged particles to transfer between the first and second display electrode, besides being able to control transfer of the colored and charged particles by a synergetic effect between a physical barrier effect by the structural wall and an electrical barrier effect by the control electrode, wherein transfer of the charged particles comprises a first process for allowing the charged particles to transfer from one of the display electrodes to the vicinity of the second control electrode and, succeeding the first process, a second process for allowing the charged particles to transfer from the second control electrode to the other display electrode side by jumping over the barrier wall or the step.
More practically, a structural barrier wall comprising a wall structure or a step structure is disposed at the boundary between the first display electrode and the second display electrode on the first substrate, and the control electrode is disposed above the structural barrier wall.
The Preferable construction comprises a shielding space In which the charged particles are able to enter and exit and which is invisible to an observer of the screen provided under the display electrode face adjoining to the step and located at the upper side of the step.
More practically, a voltage is applied to the first display electrode, the second display electrode and control electrode so that the periods satisfying the relation of (the potential of the display electrode that is not a destination of transfer)xe2x89xa7(the potential of the control electrode) greater than (the potential of the display electrode as a destination of transfer) in transfer of the positively charged particles, and satisfying the relation of (the potential of the display electrode that is not a destination of transfer) less than (the potential of the display electrode as a destination of transfer) in transfer of the negatively charged particles are involved in order to induce transfer of the charged electrode; and so that the first process satisfies the relation of (the potential of both display electrodes) greater than (the potential of the control electrode), and the second process satisfies the relation of (the potential of the display electrode before transfer) greater than (the potential of the display electrode as the destination of transfer) in transfer of the positively charged particles, and the first process satisfies the relation of (the potential of both electrodes) less than (the potential of the control electrode), and the second process satisfies the relation of (the potential of the display electrode before transfer)xe2x89xa6(the potential of the control electrode) less than (the potential of the display electrode as a destination of transfer) in transfer of the negatively charged particles, in order to induce transfer of the charged particles comprising the two processes.
Further objects, features and advantages of the present invention will become apparent from the following descriptions of the preferred embodiments with reference to the attached drawings.